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University of Nottingham, Nottingham, UK.
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Editor’s note: In randomized, controlled, clinical trials of osteoarthritis (OA), the placebo effect may be particularly important when the outcome measures are subjective – for example, the sensation of pain. In some large trials of therapeutic agents in OA, patients have responded better to active treatments than to placebo, yet the placebo has had an apparently large beneficial effect. This meta-analysis was designed to determine whether placebo has a true beneficial effect in patients with OA (by comparison of placebo-treated with untreated groups) and to identify factors that might contribute to this placebo response.